Many types of position recognition apparatus are used in fixed guideway transportation systems. However, these transportation systems operate at substantial time intervals between vehicles or trains and the position recognition systems are not required to be particularly accurate.
Conventional fixed guideway transit systems such as railways, subways, light rail systems and some automated guideway transit systems use a track circuit system for locating the position of trains or vehicles. The track is divided into sections called blocks which are insulated from each other. Each block varies in length according to the design operating speed and to the length of the typical trains. Typical block lengths will be about 2000 m. Subway systems tend to be slower and have shorter block lengths of 300 m to 1000 m. Once the train or vehicle enters the track section this can be detected by the wayside control equipment and the train presence is then transmitted to the central control computer for processing into a train control signal. In this type of system the trains are operating at 60 second to 300 second headways so the relative inaccuracy of the position location system (+/- One Block Length) is not too important.
High speed trains and short headway subways require greater accuracy, therefore these systems use a moving block system which also allows continuous steel rails to be used. The track circuit can be arranged as an inductive loop and the locomotive or other wagons can be fitted with an induction device which activates the track circuit. This approach eliminates the inaccuracy caused by the train length which is often over 400 m.
Another position location device uses the Global Positioning System (GPS) which uses geostationary satellite transmissions to determine the vehicle's location within 25 m or so. The accuracy of this system represents a major advance over traditional track circuit or moving block systems, but it can not be used in subway tunnels, inside some shielded buildings and in some geographical locations.
None of these systems is suitable for the SKYCAR PRT system since the degree of accuracy is inadequate by orders of magnitude varying from 2 to 4 ie. 100 to 10,000 times greater than the accuracy required for PRT. By the same logic none of the previous or existing transportation systems have used bar coding in this way to form a train or vehicle control system. This is because they never required the degree of accuracy in position location.
Bar Codes and Laser Scanners are also widely used in the identification of vehicles or materials being transported on a fixed guideway. For example bar codes are used in railway freight wagon location. The bar code is attached to the wagon and a trackside reader transmits the wagon's identity to a control center. Bar codes are also used in airport baggage systems to track baggage carts in automated baggage systems. Barcodes are also used on packages carried by conveyor belts with the bar code reader located stationary beside the belt. Barcode readers are also stationed beside industrial assembly lines to monitor and control bar coded parts flow.
No industrial or transportation system to our knowledge mounts the bar code scanner on the moving vehicle and arranges the bar code in a sequential strip in the guideway. This invention is the basis of this claim.